DE 10 2006 004 313 A1 discloses an electric motor with a rotor and a stator, which has an external part and an internal part, which are arranged concentrically to a rotation axis and can be adjusted rotationally in relation to each other about the said rotation axis. The known electric motor is designed as an external rotor motor, so that the external part forms an external rotor and the internal part forms an internal stator. The external rotor is assembled from four permanent magnets. The internal stator has four pole arms, which each bear an electric coil. The known electric motor is overall designed to be symmetrical in the circumferential direction.
In order to make it easier for an electric motor to start up, it is known from U.S. Pat. No. 7,345,440 B2 to make an air gap that forms radially between the internal rotor and the external stator in such an electric motor asymmetrical in the circumferential direction. For example, the air gap can taper in a continuous or stepped manner in the circumferential direction. A pole shoe on the stator side can likewise include a longitudinal groove or be designed to be unequal or asymmetrical in the circumferential direction. In the known electric motor, the asymmetries are always realised by an asymmetrical design of the stator, while the rotor is symmetrical.
FR 2 945 388 A1 discloses a further electric motor in which an asymmetry is realised by combining an internal rotor that bears four permanent magnets with an external stator that bears three or six coils.